1. Technical Field
The present invention relates to the characteristic layout of constituent elements that make up an electro-optical device (apparatus). The electro-optical device to which the invention is directed has electro-optical elements such as light-emitting elements made of organic electroluminescent (EL) material or the like. The invention further relates to an electronic apparatus that is provided with such an electro-optical device.
2. Related Art
The above type of electro-optical element changes its gradation (typically, luminance) when a current is supplied thereto. In this respect, a configuration for controlling the current supplied thereto (hereafter referred to as a “driving current”) by means of a transistor (hereafter referred to as a “driving transistor”) is known in the art. Disadvantageously, the known configuration has a problem of nonuniformity among the gradations offered by electro-optical elements. That is, the gradations could vary from one electro-optical element to another because of the individual specificity (i.e., difference) of driving transistor characteristics, in particular, differences in threshold voltages thereof. In order to reduce nonuniformity in gradations, for example, JP-A-2003-332072 (specifically, FIG. 1 thereof) and JP-A-2006-30635 (specifically, FIGS. 1-3 thereof) disclose a technique for compensating for differences in the threshold voltages of the driving transistors.
FIG. 17 is a circuit diagram that illustrates the configuration of a pixel circuit P0 that is described in JP-A-2003-332072. As illustrated in FIG. 17, a transistor Tr1 is interposed between the gate electrode of a driving transistor Tdr and the drain electrode thereof. One terminal of a capacitative element C1, specifically, an electrode L2 thereof, is connected to the gate electrode of the driving transistor Tdr. A retention volume C2, in other words, a hold capacitor, is a capacitance interposed between the gate electrode of the driving transistor Tdr and the source electrode thereof. A transistor Tr2 is a switching element that is interposed between a data line 103 and the other terminal of the capacitative element C1, an electrode L1, so as to switch conduction (i.e., continuity)/non-conduction between the data line 103 and the electrode L1 of the capacitative element C1. The data line 103 supplies a potential (i.e., voltage) VD that is in accordance with luminance specified for an organic light-emitting diode element 110. The potential VD according to the specified luminance is hereafter referred to as a “data potential”. The organic light-emitting diode element 110 is hereafter abbreviated as an “OLED element” 110.
The operation of the above-described configuration is explained below. As the first step, a signal S2 is supplied to turn the transistor Tr1 into an ON state. When the driving transistor Tdr is “diode-connected” through the transition of the transistor Tr1 into an ON state, the gate potential of the driving transistor Tdr converges into “VEL−Vth” (where “Vth” denotes the threshold voltage of the driving transistor Tdr). As the second step, a signal S1 is supplied to turn a transistor Tr2 into an ON state while turning the transistor Tr1 OFF. With such an ON/OFF setting, electrical conduction between the electrode L1 of the capacitative element C1 and the data line 103 is established. Through the above operation, the potential of the gate electrode of the driving transistor Tdr changes from the immediately previous voltage level by the level amount calculated by dividing the potential change that occurs at the first electrode L1 of the capacitative element C1 in proportion to the ratio of an electrostatic capacity (i.e., capacitance) of the first capacitative element C1 to an electrostatic capacity of the retention volume C2. That is, it changes by the level amount in accordance with the data potential VD. As the third step, a signal S3 is supplied to turn a transistor Te1 into an ON state while turning the transistor Tr2 OFF. As a result of the above operation, a driving current Iel that does not depend on the threshold voltage Vth is supplied to the OLED element 110 via the driving transistor Tdr and the transistor Te1. The fundamental principle adopted in JP-A-2006-30635 for compensation of the threshold voltage Vth of the driving transistor Tdr is the same as above.
As illustrated in FIG. 18, for example, in the layout of the above-described pixel circuit, the first capacitative element C1 is arranged between the data line and a power line. For this reason, parasitic capacitance is generated between a conductor wiring that constitutes the first capacitative element C1 and another conductor wiring that constitutes the data line 103. In particular, when a crosstalk is generated between the first capacitative element C1 and the data line 103 via the generated parasitic capacitance so as to change the voltage of the first capacitative element C1, the gate potential of the driving transistor Tdr changes. This causes a change in the driving current Iel in accordance with the changed gate potential. For this reason, the luminance of the OLED element 110 changes.
The pixel circuit described in JP-A-2006-30635 is configured to have a metal shield that surrounds the capacitative elements C1 and C2, thereby minimizing the electric field effects of the data line. However, disadvantageously, such a configuration requires an additional space for providing the metal shield, which makes it more difficult to achieve a high degree of integration of elements.